1. Field of the Invention
The present invention relates generally to set retarding additives, hydraulic cement compositions containing the additives and methods of using the set retarded cement compositions for cementing subterranean zones in oil, gas and water wells.
2. Description of the Prior Art
Hydraulic cement compositions are used for carrying out various operations in oil, gas and water wells including, but not limited to construction and completion operations such as primary cementing and remedial operations such as squeeze cementing. Primary cementing involves the placement of a hydraulic cement composition into the annular space between the walls of a well bore and the exterior of a pipe such as casing disposed therein. The cement composition is pumped into the annular space and allowed to set into an annular cement sheath therein whereby the pipe is bonded to the walls of the well bore by the set cement.
Squeeze cementing techniques usually involve the undesirable movement of oil, gas or water through small holes or cracks in pipe disposed in the well bore; holes, cracks, voids or channels in the annular cement sheath between the pipe and the well bore; annular spaces between the cement sheath and the pipe or the walls of the well bore and permeable zones or fractures in subterranean formations. Such holes, cracks, etc. are plugged by squeezing hydraulic cement compositions therein which harden and form impermeable plugs.
In performing cementing operations in oil, gas and water wells, the cement compositions are often subjected to high temperatures, particularly when the cementing is carried out in deep subterranean zones. The high temperatures can cause premature setting of the cement compositions, i.e., the compositions can not be pumped for long enough times before setting to place them in the zones to be cemented. This requires the use of set retarding additives in the cement compositions which extend the setting times of the compositions so that adequate pumping time is provided in which to place or displace the compositions into desired subterranean zones.
While a variety of cement set retarding additives have heretofore been developed and utilized, the additives frequently produce erratic results in cement compositions of different component make-up and/or cause premature gelation of cement compositions in the hostile high temperature environments to which the cement compositions are subjected. The high temperatures referred to herein are temperatures up to 250.degree. F. and higher, and the gelation referred to is the abnormal increase in viscosity of a cement composition without a significant increase in compressive strength. The increase in viscosity makes the cement composition difficult or impossible to pump even though the cement composition has not set. In addition, prior art set retarding additives comprised of materials such as lignosulfonates and synthetic polymers are often expensive to produce.
Thus, there is a need for improved cement set retarding additives, set retarding cement compositions and methods of cementing zones in oil, gas and water wells. In particular, there is a need for improved set retarding additives which are relatively inexpensive and bring about predictable cement composition setting times in the hostile subterranean environments encountered in wells.